This application requests a supplement to an ongoing grant, Modeling Viral and T Cell Dynamics. Mathematical modeling combined with experiment has led to increased understanding of the processes that underlie HIV-1 infection as well as improved therapies. Infection by hepatitis C virus (HCV) and hepatitis B virus (HBV) continue to cause liver failure and hepatocellular carcinoma in infected individuals. Understanding the basis of pathogenesis and the development of potent antiviral therapies for these viruses lag behind our advances in HIV. We propose to expand our efforts in modeling HCV and HBV in vivo kinetics and the effects of antiviral therapy. In the case of HCV we propose to develop realistic models of new treatments using pegylated interferon a2b, assess effectiveness of current once a week dosing and compare it to alternative dosing regimes. For HBV we propose to both develop new dynamic models of infection as well as to examine with modeling the effectiveness of therapies involving combinations of antiviral agents. Our goal in all of these analyses is to gain basic understanding and help move that understanding into new treatments. [unreadable] [unreadable]